The present invention pertains to pre-cutover switching system testing and more particularly to an arrangement for isolation of a single line for line verification and ring testing.
When a new switching system, such as a GTD-5 EAX, is installed to replace an existing switching system such as a step-by-step system, there is a testing interval during which time the subscriber's cables are double jumpered to both switching systems. That is, each subscriber line will have an appearance on an inlet to each switching system. This double jumpering arrangement is made at the main distribution frame.
Without special provisions, the line of each subscriber would be connected to a battery feed device from each switching system. Connection of the subscriber's line to battery feed devices of both switching systems would produce a shunting effect and result in improper signaling and supervisory functions, as well as affecting the quality of voice transmission. Therefore, selective isolation of the subscriber's line from these battery feed devices is highly desirable. During the testing interval, it is also desirable to selectively switch the application of the battery feed signal between the two switching systems.
Accordingly, it is the object of the present invention to isolate particular subscriber lines in a pre-cutover environment for line verification and ring testing.